1. Field
One or more embodiments of the present disclosure relate to an image forming apparatus, and more particularly, to an image forming apparatus with an improved paper feeding device for feeding a recording medium.
2. Description of the Related Art
Image forming apparatuses are generally used to form an image on a recording medium. Examples thereof include printers, copy machines, facsimile machines, and all-in-one devices implemented by combining functions of a printer, a copy machine, and a facsimile machine.
Such image forming apparatuses generally include a paper feeding device for feeding a recording medium to a printing unit included in the image forming apparatus. The recording medium accommodated in the paper feeding device is picked up by a pickup roller and fed to the printing unit along a predetermined path. The pickup roller picks up the recording medium by using a frictional force against the recording medium. A frictional force sufficient for the pick-up requires a predetermined pressure relationship between the recording medium and the pickup roller. For the predetermined pressure relationship, a knock-up plate for pressing the recording medium against the pickup roller is used.
However, because the knock-up plate presses the recording medium against the pickup roller even when the paper feeding device is withdrawn, a so-called jamming phenomenon occurs in which a portion of the recording medium is jammed because the recording medium remains due to the frictional force between the recording medium and the pickup roller, thereby resulting in faulty printing.
To solve this problem, a method of releasing the pressure relationship between a recording medium and the pickup roller by lowering the knock-up plate when the paper feeding device is withdrawn has been proposed.
Conventionally, by fixedly assembling a guide unit for guiding the knock-up plate to be lowered in a main body to lower the knock-up plate assembled with the paper feeding device along the fixed guide unit when the paper feeding device is withdrawn according to the method, a pressure relationship between the recording medium and the pickup roller can be released.
However, because the guide unit has a fixed structure and provides a constant slope regardless of the remaining number of recording media accommodated in the paper feeding device, a gap between the guide unit and the knock-up plate varies according to the remaining number of recording media. In particular, when the remaining number of recording media is large, the gap between the guide unit and the knock-up plate is very large, and thus, the knock-up plate cannot be immediately lowered even when the paper feeding device is withdrawn and the pressure relationship is temporarily maintained, thereby resulting in a jam.